linux-kernel - Re: [PATCH] media: pci: ttpci: av7110: avoid compiler optimization of reading data[0] in debiirq()

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Date:   Wed, 9 Sep 2020 10:55:04 +0200
From:   Pavel Machek <pavel@....cz>
To:     Sean Young <sean@...s.org>
Cc:     Jia-Ju Bai <baijiaju@...nghua.edu.cn>, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: pci: ttpci: av7110: avoid compiler optimization
 of reading data[0] in debiirq()

On Sun 2020-08-30 09:30:36, Sean Young wrote:
> On Sun, Aug 30, 2020 at 04:20:42PM +0800, Jia-Ju Bai wrote:
> > In debiirq(), data_0 stores the value of data[0], but it can be dropped
> > by compiler optimization. Thus, data[0] is read through READ_ONCE().
> > 
> > Fixes: 6499a0db9b0f ("media: pci: ttpci: av7110: fix possible buffer overflow caused by bad DMA value in debiirq()")
> > Reported-by: Pavel Machek <pavel@....cz>
> 
> Pavel reported that your patch was garbage, if you are trying to defend
> against a malicious pci device. READ_ONCE() will not help here.

I would not use exactly those words, but agreed; we should have some
explanation that it is feasible to protect against malicious av7110
device, first.

Best regards,
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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